1. Field of the Invention
This invention relates to a new and improved method and apparatus for monitoring a fluid system, and is particularly suitable for use with high pressure liquid chromatography (HPLC) pumps having active rear seal washing.
2. Description of Related Art
High pressure liquid chromatography (HPLC) generally requires the components of a sample to be separated or analyzed be dissolved in a mobile phase liquid, termed an eluent, and conveyed by that liquid to a stationary phase, that is, a chromatography column. HPLC eluent delivery systems are used to supply the liquid and deliver the liquid, with dissolved sample, to the column. Selected pressures ranging from substantially atmospheric pressure to pressures on the order of ten thousand pounds per square inch are common to force the liquid into the column. Specially designed HPLC pumps are used to withstand extreme pressures and to deliver the liquid at precisely controlled flow rates in a smooth and uniform manner.
HPLC pumps are generally piston pumps with plungers formed of sapphire or ceramics. The pump heads include special high pressure seals that may have lips pressed against the plunger surface by the pressure built up in the pump head, that is, the system pressure. As the piston moves to aspirate new eluent, small amounts of eluent residing in the head chamber of the pump are commonly transported by the piston surface through the seal to the backside of the seal. This leaking amount is normally so small that it evaporates and does not disturb the pumping process.
Salt-containing eluents are commonly used, especially in biochemical applications. However, if the pumped eluent contains such salts, such evaporation may cause problems, because after a few pump strokes, salt crystals may build up on the backside of the seal. Such crystals are often sharp and can destroy the seal surface within a few piston strokes. In order to prevent the growth of salt crystals on the rear side of the seal it is common practice to keep the piston wet via a wash chamber filled with an aqueous wash solution, which is sometimes spiked with organic solvent. This organic addition to the wash solution prevents growth of algae and fungi inside the wash chamber.
Such wash chambers must be maintained as the wash solution becomes contaminated by the pumped eluent leaking through the seal. If not regularly replaced, the wash solution can become very salty and so precipitate which could destroy the sealing. Conventionally, wash solution within the wash chamber is replaced using a manual syringe fluidly connected to the wash chamber. Disadvantageously, washing by a hand syringe requires the operator to remember to replace the wash solution on a regular basis. Typically, wash solution replacement is done in a haphazard manner and the seal wears out prematurely.
Some advanced wash designs include a small auxiliary pump which transports fresh wash solution into and through the wash chambers at regular time intervals. Such advanced designs are sometimes referred to as active back seal washing. The wash solution replacement cycle depends on the salt load and the pressure at which the HPLC pump is run. As biochemical applications are increasingly common, salt-containing eluents are more popular than ever. As a consequence, such active seal washing is becoming increasingly popular.
Another increasingly popular concept is wellness, that is, preventive maintenance monitoring. Preventive maintenance monitoring is highly desirable in HPLC systems as uptime is an overwhelming criterion of HPLC systems. In many cases downtime implies lost samples, which in the pharmaceutical industry can be very costly. Furthermore, if production quality control is down in the pharmaceutical industry, drug production would be blocked immediately. Thus, preventive maintenance monitoring of HPLC systems is highly desirable because HPLC is the standard method used in pharmaceutical production quality control.
HPLC pumps contain several wear parts, which must be replaced periodically. The most stressed wear part in a HPLC pump is the high pressure seal. As a HPLC pump contains at least two pistons, there are two seals which must be regularly replaced. Such seals are expected to survive millions of piston strokes at high friction. Undetected seal wear is by far the most frequent reason for unexpected pump downtime. Furthermore, undetected seal wear may impair the quality of the analysis, and even permanently damage other expensive parts of the HPLC pump. For example, the wash solution can eventually run into the ball bearings of a piston pusher and cause the destruction thereof.
What is needed is a leakage monitoring for a system including a high pressure seal which overcomes the above and other disadvantages of known systems including a high pressure seal.
In summary, one aspect of the present invention is directed to an apparatus including a liquid chamber, a wash chamber, a reservoir, a supply pump, a return line, and a detector. The liquid chamber includes a seal for sealing a liquid within the liquid chamber. The wash chamber is located adjacent the seal. The reservoir supplies a wash solution to the wash chamber. The supply pump supplies a unidirectional flow of wash solution from the reservoir to the wash chamber. The return line conveys a return flow from the wash chamber to the reservoir, in which the return flow includes any leakage of the liquid from the liquid chamber into the wash chamber and the portion of the wash solution that returns from the wash chamber to the reservoir. The detector determines whether there is a differential between the unidirectional flow and the return flow.
In one embodiment, the liquid chamber is a pump chamber of a high pressure liquid chromatography (HPLC) pump. The HPLC pump may include a piston extending through the pump chamber, the seal, and the wash chamber. The apparatus may include one, two, three or more liquid chambers and corresponding one, two, three or more wash chambers, in which each of the liquid chambers includes a seal, and each of the wash chambers is adjacent a respective one of the seals.
Preferably, the supply pump is a peristaltic pump. Preferably, the detector is a drop counter. In one embodiment, the detector includes a cap releasably engaging the reservoir, a return passageway for fluid connection with the return line, the return passageway extending through the cap, and a pair of spaced electrodes extending through the cap and into the reservoir, the ends of the electrodes are positioned below the return passageway such that a drop of wash solution falling from the return passageway into the reservoir bridges a space between the ends as the drop passes the ends.
The apparatus may include a detection circuit, to which the electrodes are operably coupled for monitoring the number of drops of wash solution that pass between and bridge the space between the electrodes. The detection circuit may monitor the operational state of the supply pump. The detection circuit may provide a first signal indicating that the supply pump is running and the detector senses drops of return flow entering the reservoir. The detection circuit may provide a second signal indicating that the supply pump is running and the detector does not sense drops of return flow entering the reservoir. The detection circuit may provide a third signal indicating that the supply pump is not running and the detector senses drops of return flow entering to the reservoir. The detection circuit may provide a fourth signal indicating continuous conductivity between the electrodes.
Another aspect of the present invention is directed to a method of monitoring leakage in a system including a liquid chamber, a seal for sealing a liquid under within the liquid chamber, and a wash chamber adjacent the seal. The method includes the steps providing a unidirectional flow of a wash solution from a reservoir to the wash chamber and determining whether there is a differential between a return flow and the unidirectional flow, the return flow including any leakage of the liquid from the liquid chamber into the wash chamber and the portion of the wash solution that returns from the wash chamber to the reservoir.
The method may include the step of providing a first signal indicating that the return flow is above a predetermined threshold based upon the unidirectional flow. The method may include the step of providing a second signal indicating that the unidirectional flow is greater than the return flow. The method may include the step of providing a third signal indicating that the unidirectional flow is less than the return flow. The method may include the step of providing a fourth signal indicating that the level of the reservoir exceeds a predetermined level.
An object of the present invention is to provide a method and apparatus for monitoring a fluid system.
Another object of the present invention is to provide a method and apparatus of the above character for use with a high pressure liquid chromatography (HPLC) pump having an active rear seal washing system.
Yet another object of the present invention is to provide a method and apparatus of the above character suitable for continuous leak monitoring for determining a state of seal degradation.
It is a further object of the present invention to provide a method and apparatus of the above character for monitoring the operational state, or wellness, of the active rear seal washing system.